The present invention relates to a method and an apparatus for controlling an attitude of a shield excavator to excavate a curved tunnel or to change the direction of advancing the excavator.
A shield excavator has a plurality of thrust jacks in a circumferential direction of a shield frame for advancing the excavator. Advancement of the excavator is carried out by extending piston rods of the jacks through supply of pressurized working oil into the jacks with their rear ends being securely supported by segments.
In order to curvedly advance the excavator, some of the jacks are supplied with enough pressurized working oil to extend their piston rods while the remaining jacks are supplied with no working oil or supplied with working oil pressurized to the extent that no thrust force is imparted to the excavator. That is, as to the remaining jacks, no-load following operation is carried out such that their piston rods extend merely to follow the advancement of the excavator.
FIG. 1 shows a hydraulic circuit of a conventional automatic directional control system for use with the above-mentioned conventional shield excavator. A hydraulic pump 2, which pumps oil from a storage tank 1 and pressurizes the same, is connected at its discharge port to an end of a pipeline 3 the other end of which in turn is connected to a main selector valve 4. The valve 4 is connected through a return pipeline 5 to the tank 1 so as to return the working oil.
The valve 4 is further connected with two pipelines 6 and 11. The pipeline 6 is branched into pipelines 7a and 7b which in turn are respectively communicated with head-side oil chambers 22a and 22b of thrust jacks 10a and 10b through jack load pressure selector valves 8a and 8b and pipelines 9a and 9b. The pipeline 11 is branched into two pipelines 12a and 12b which are respectively communicated with rod-side oil chambers 23a and 23b of the jacks 10a and 10b.
A no-load following valve block 13 comprises a pressure reducing valve 15 for reducing the pressure of the working oil from the selector valve 14, a pipeline 16 for passage of the working oil from the reducing valve 15 and check valves 17a and 17b for preventing the working oil from returning to the valve 15. The pipeline 6 is connected to the selector valve 14 through a pipeline 18. The check valves 17a and 17b are connected to the pipelines 9a and 9b through pipelines 19a and 19b.
The pipelines 19a and 19b are connected to the tank 1 through a pipeline 20 with check valves 21a and 21b. Reference numerals 24 and 25 denote safety valves. It is to be understood that many thrust jacks 10 are disposed side by side in practice though only two jacks 10a and 10b are shown in FIG. 1. Set pressures P.sub.1, P.sub.2 and P.sub.3 of the safety valves 24 and 25 and the pressure reducing valve 15, respectively, are adjusted to satisfy the following condition: EQU P.sub.1 .apprxeq.P.sub.2 &gt;&gt;P.sub.3
FIG. 2 illustrates a typical operation control board 26 of conventional shield excavators. The board 26 comprises a plurality of equiangularly spaced jack selection switches 27 (12 switches are shown in FIG. 2) which are disposed in the form of ring correspondingly to the thrust jacks, rotational moment directional pilot plates 28 (24 pilot plates are shown in FIG. 2) disposed in positions correspond to the switches 27 and correspond to midways between the switches 27, and a jack operation unit 32 comprising push, pull and stop switches 29, 30 and 31. The board 26 further has a load pressure indicator 33, a left jack stroke meter 34, a right jack stroke meter 35 and a pitching indicator 36 (or inclinometer in the axial direction).
When the selection switch 27 is pushed, the switch 27 lights on and correspondingly a command signal is outputted to a valve unit 37 so as to change over the selector valves 8a and 8b of the corresponding jacks 10a and 10b to the load pressure side. When the push switch 29 is pushed, the switch 29 lights on and correspondingly a command signal is outputted to the valve unit 37 so as to change over the main selector valve 4 to the push side, whereby the piston rods of the selector valves 8a and 8b having been changed over to the load pressure side are extended in unison for excavation. When the switches 27 and 29 are pushed again, they light off and the respective selector valves 8a, 8b and 4 are changed over to neutral positions (or closing sides).
When the shield excavator is to be advanced straightforwardly, all the jack selection switches 27 are pushed to light on so that all the selector valves 8a and 8b are changed over to the load pressure sides. Then the push switch is pushed to light on so that the main selector valve 4 is changed over to the push side. As a result, all the jacks 10a and 10b are concurrently extended to straightforwardly advance the excavator for excavation.
When excavation of a curved tunnel or correction in direction of advancing the shield excavator is required, an operator turns off some of the jack selection switches 27, which correspond to the jacks in the direction of orienting the excavator. As a result, the corresponding selector valves 8a and 8b are changed over to their neutral positions so that the corresponding jacks 10a and 10b are de-energized and consequently a rotational moment is imparted to the excavator.
Whether a desired attitude is attained or not is checked by the left and right jack stroke meters 34 and 45 as to the left and right directions and by the pitching meter 36 as to the upward and downward directions. When the excavator is inclined to much or too less in the upward or downward direction and/or is directed too much or too less in the right or left direction, such deviation is compensated by accordingly increasing or decreasing the number of jacks to be energized.
Which jacks are to be energized is determined as follows. From a total thrust required to advance the excavator, a required minimum thrust jack number (in general more than half of all the thrust jacks) is determined. Thrust jacks to be energized are selected in a jack pattern or arrangement such that the required rotational moment is obtained with the thrust jacks being greater in number than the minimum number and as many as possible and being in dispersed pattern so as not to burden locally concentrated load to the segments.
According to such prior art system, the number of the jacks to be energized is determined depending upon a required total thrust; and the jacks to be energized are experientially selected in view of combined vertical and horizontal moments. In order to minimize meandering movements of the excavator and to attain a high degree of accuracy of a finished tunnel, any positional error and attitudinal deviation of the shield excavator must be compensated as soon as possible. Therefore, the rotational moment must be changed little by little, which requires random jack selection. The jack selection is conventionally effected by an operator's own judgment so that it is much difficult and requires a skilled operator.
In a further conventional system, gyroscopic or laser-type automatic position and attitude sensors are equipped. In response to signals from the sensors, thrust jacks are controlled to carry out automatic direction control of a shield excavator. Also in this case, jack patterns or combinations to be selected are so many that algorithm of selecting jacks to be energized is too complicated.
In view of the above, a primary object of the present invention is to provide a method and apparatus for controlling the attitude of a shield excavator which can simplify and automate the control of the attitude of the shield excavator and which can be operated by an ordinary operator not by a skilled operator because operation steps which requires the operator's judgment are minimized.